The present invention relates to a syringe useful for delivering fluid to a fluid receiving device such as a balloon catheter, and more particularly, concerns a syringe for such use with pressure-limited delivery capacity.
Syringes are commonly utilized by physicians, surgeons and other medical personnel for a variety of situations involving the delivery of fluid. One particular situation involves the inflation of a balloon catheter which is intended to be positioned inside a blood vessel of a patient, and then inflated to a sufficient degree to occlude the path of the blood vessel. This balloon catheter is generally injected with a fluid through an insertion tube or catheter by means of a syringe inserted in and connected to the end of the tube which may extend outside of the patient. However, inasmuch as the balloon portion of the catheter is confined within the blood vessel of the patient, inflating the same can oftentimes be a matter of guesswork since the balloon cannot be seen by the operator during its inflation. It can be appreciated that, without proper controls or monitoring means, such a balloon catheter can easily be underinflated or overinflated. Underinflation of a balloon catheter inside the blood vessel will result in a loose fit therewithin so that the balloon itself is not snugly confined against the walls of the blood vessel. With this condition, the balloon is prone to migration within the blood vessel, which is clearly undersirable. On the other hand, overinflation of the balloon may result in its rupture during inflation or may result in a condition of being overstressed so that premature failure of the balloon while in the blood vessel may occur. This condition also is undesirable. Accordingly, the filling of a fluid receiving device, particularly a fluid-sensitive balloon catheter, by a syringe can be problematical without a control or monitoring mechanism to assist the operator in determining the proper amount of fluid for optimum inflation of the fluid receiving device.
There have been attempts to rectify this deficiency, particularly in the inflation of balloon catheters, by the utilization of various control devices. For instance, U.S. Pat. Nos. 4,147,170; 4,116,201 and 3,799,171 all disclose devices for controlling the inflation of balloon catheters. However, the devices disclosed in these patents all rely upon a valve or valving mechanism to open and close at the appropriate pressure levels for controlling the amount of fluid to be delivered to the balloon catheter. Another patent, namely U.S. Pat. No. 4,000,741, discloses a syringe useful for pumping fluid into a body cavity of a patient or into a fluid receiving device, which relies upon a flexible balloon secured to an extension member at the tip of the syringe. This balloon inflates at a pre-determined pressure level to relieve pressure generated by the syringe so as to control the level of pressure being pumped into the fluid receiving device. The devices described in conjunction with the aforementioned patents, while attempting to resolve the need to control the inflation pressure into the balloon catheter, oftentimes involve somewhat complex structure in their manufacture with resultant increase in production cost and quality control procedures. Moreover, use of valving mechanisms and inflatable balloons at the tip of the syringe adds another element to the structure of this type device with the concomitant risk that such an additional element may fail during use to the detriment of the patient. Accordingly, simplified improvements in a syringe for controlling the amount of fluid for delivery to a fluid receiving device are still being sought. The present invention is directed to that end, and satisfies the need for such a syringe with a pressure controlling provision.